Dynamische Ergodisierung an TEXTOR-94: Konzeptanalyse und Auslegungsuntersuchung

Haßler, M.

Book/Report

FZJ-2019-04564

Dynamische Ergodisierung an TEXTOR-94: Konzeptanalyse und Auslegungsuntersuchung

Haßler, M. (Corresponding author)FZJ*

1998
Forschungszentrum Jülich, Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich, Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3616, VI, 139 p. (1998)

Please use a persistent id in citations: http://hdl.handle.net/2128/22652

Report No.: Juel-3616

Abstract: At the Forschungszentrum Jülich a coil system for magnetic ergodisation of the plasma edge is to be built in TEXTOR-94: the Dynamic Ergodic Divertor (DED). The helical coils will be installed at the high field side inside the vacuum vessel. They are aligned inparallel to the rnagnetic field lines in the plasma at the q=3 surface. The system will be fed by multiphase current to distribute the expected heat load an the divertor target plates over a wider area and e.g. to influence plasma rotation at higher frequencies. The aims of this thesis are to analyse different possible concepts for such a coil arrangement and to lay out selected DED components and thereby to contribute essentially to the final technical solution. The layout development is accompanied by field calculations ofthe different possible system designs. The path of the coils is calculated by means of the field line helix. A four phase current system with sixteen coils proves to be the most favourable; by connecting pairs of coils carrying opposite currents in series less power supplies (IGBT based) are needed. A coil design of complete turns has the advantage of a higher flexibility regarding the operation mode selection and needs less space than a module system. The coil outlets will be bundled to reduce the number of required hanges; additional coils above and below the ergodisation coils compensate the resuiting asymmetry in the poloidal current distribution. The TEXTOR-94 liner has to be modified in order that the perturbation coils can be installed. The coil cables are designed for amperages up to 15 kA and frequencies up to 10 kHz and consist of bundles of polyimide insulated copper wires in a corrugated stainless steel tube. Transformers adapt the electrical data of the power supplies to the needs of the ergodisation coils. Capacitors in series connection supply the coil system with reactive power. A special decoupling transformer compensates the mutual transfer of active power between the 90° phase shifted current systems. Ohmic losses of the coil current and radiation of the surrounding wall materials lead to a temperature rise of the coils. To remove the heat, a gas cooling system will be laid out in this paper. Because of its higher heat capacity compared to helium, air is chosen as coolant. It is possible to achieve the desired heat removal with the proposed cooling system; however the necessary technical efforts led to a further development of the cooling concept. Numerical field calculation methods are used to analyse the effect of the Dynarnic Ergodic Divertor at different modes of operation (rn/n = 12/4, 6/2, 3/1 and mode mixing). With increasing perturbation current the induced magnetic islands (main modes, higher harmonics, and satellite islands) grow. At maximum current, they are destroyed to a great extend in the plasma edge region, where a wide ergodic zone exists. A first analysis of field line trajectories shows that for field line diffusion calculations three zones should be distinguished: the region of strong stochastisation, the remains of the embedded islands, and the unperturbed region at the lote- field side. The difference between the calculated island width using standard theory and the measured width of the islands in the Poincare plots ean be corrected using weighted Fourier coefficients in the standard formula.

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